Investigations on organic fungicides

Summary The antimicrobial spectrum of the antifungal substance tetramethylthiuram disulphide (t.m.t.d.) was determined. The substance in general possessed antifungal rather than antibacterial properties. The bacteria as well as the moulds varied considerably with regard to their sensitivity towards t.m.t.d. Among the moulds the parasitic species were in general more sensitive to t.m.t.d. than the saprophytic fungi.The mode of action of t.m.t.d. was briefly discussed. It was concluded that this substance probably acts by interference with the anabolic part of mould metabolism.     

Investigations on organic fungicides

Antonie van Leeuwenhoek - The antimicrobial spectrum of the antifungal substance tetramethylthiuram disulphide (t.m.t.d.) was determined. The substance in general possessed antifungal rather than...     

Investigations on fungicides

The systemic anti-mildew activity shown by homologous series of alkoxy-, alkylamino- and alkylthio-trichloroethyl formamides when applied to the roots of wheat or cucumber seedlings has been measured. In general the thio compounds were much less active than their oxy and amino analogues. The alkyl grouping giving most activity varied from one series to another and with test method. In cucumber plants the most prolonged protection against mildew was given by the sec-butoxy and sec-butylamino compounds. When inoculated disks of cucumber leaf tissue were floated upon solutions of the compounds, smaller differences in anti-mildew activity were found than when application was made through the roots.     

Investigations on fungicides

A series of pyrazole derivatives, which are structural analogues of the systemic fungicide, carboxin (5,6-dihydro-2-methyl-i,4-oxathiin-3-carboxani-lide), have been synthesized and their antifungal properties investigated. 3,5-dimethylpyrazole-i-carboxanilides, although active in vitro and in leaf disk tests, showed no systemic antifungal activity. Certain 3,5-dimethylpyra-zole-4-carboxanilides, however, and their corresponding 1 -methyl derivatives, showed good activity in spore germination tests and high activity against wheat and broad bean rusts in vivo. In several instances, systemic antifungal activity was of the same order as that of carboxin, although generally accompanied by higher levels of phytotoxicity. 1 -Phenyl derivatives were essentially inactive. Substitution in the anilide ring by 3-methyl, 2-methyl or 3-chloro groups resulted in enhanced systemic activity, while 4-chloro, 4-ethoxy, 2-nitro and 3,4-dichloro substituents reduced activity.     

Investigations on fungicides

A number of bis-[(i-formamido-2,2,2-trichloro)ethylamino]-alkanes and their dioxy and dithio analogues were examined for direct and systemic antifungal activity. All compounds showed very low in vitro fungitoxicity and only slight protectant anti-mildew activity when applied as a foliar spray. Certain diamino and dioxy derivatives were, however, systemically active against powdery mildew fungi when applied as a root drench to seedlings of wheat or cucumber; the dithio analogues were inactive. The level of systemic activity shown by these compounds was markedly influenced by the nature of the hydrocarbon ‘bridging’ group.     

Investigations on fungicides.

Uninoculated roots of pea (Pisum sativum) and French bean (Phaseolus vulgaris) have been shown to exude a number of antifungal compounds when grown in a non-sterile aqueous aerated medium. These have been identified and their possible importance in relation to disease resistance is discussed.     

Investigations into the cytokinin-like properties of benzimidazole -derived fungicides

Of seven systemic benzimidazole fungicides tested, four showed cytokinin activity in a modified Amaranthus betacyanin bioassay. In the presence of the gibberellins A₄ and A₇, in the dark at 25°C, the four active compounds stimulated the germination of seeds of two celery cultivars dependent on cytokinin for germination under these conditions. One cytokinin-active fungicide was methyl benzimidazol-2-yl carbamate (MBC) and the other three break down into this compound in solution. The three inactive fungicides do not. However, the hormonal properties of the cytokinin-active fungicides may not be due to the MBC moiety alone because sometimes they were more cytokinin-active than pure MBC.     

Investigations on fungicides: X. The antifungal activity of 2-deoxy-D-glucose

The fungitoxicity of 2-deoxy-D-glucose was examined in spore germination tests using Botrytis cinerea, B. fabae, Alternaria brassicicola, Aspergillus niger, Cladosporium cucumerinum, C. fulvum, Sclerotinia fructigena, Verticillium albo-atrum and Glomerella cingulata. It proved to be toxic, at concentrations below 10 μg./ml., to all of these fungi except G. cingulata which was resistant to concentrations up to 2000 μg./ml. The effect of a-deoxy-D-glucose on the mycelial growth of these fungi was assessed and again G. cingulata proved to be resistant to high concentrations of the compound, as also did A. niger.
The results are discussed in relation to the known inhibitory nature of 2-deoxy-D-glucose in other systems.